confluens and the Morphology of the Ascocarp. 379 
filament, and use in furnishing energy for carrying out helio¬ 
tropic reactions and building cell walls is any different than 
the corresponding processes in a pollen-tube or a uninucleated 
cell of Spirogyra. It is probable, as noted above, that the 
nuclei are centres for the internal metabolism of the cell, but 
there is no evidence that they influence its absorption of food- 
materials by osmosis and its excretion of wastes any differently 
in the uninucleated than in the multinucleated condition. It 
is quite conceivable that any cell of the leaf-mesophyll should 
perform all its starch-building functions in entire independence 
of its neighbours, even to the extent of consuming its own 
product and excreting the wastes, but we cannot conceive any 
particular uninucleated area (energide) in a Vaucheria filament 
acting in such perfect independence of neighbouring areas, 
simply because in the latter case the uninucleated area is not 
an osmotic unit, but only a part of a larger osmotic system 
bounded by a single plasma-membrane. The mesophyll-cell 
in these respects is comparable to the entire Vaucheria 
filament. 
In Volvox the income and outgo can be considered for each 
individual of the colony separately, and can vary in each 
according to the individual peculiarities of the cells, while for 
the so-called energides of Botrydium no such conception is 
possible. The income and outgo of the whole mass is regulated 
by a common plasma-membrane. Even assuming that the 
strands of protoplasm which extend between the neighbouring 
cells in many tissues really represent continuity and not 
merely contact of the protoplasm of the respective cells, the 
case would not be materially altered, since the extreme 
tenuousness of such strands in most cases would prevent their 
serving as channels for any rapid interchange of food-materials, 
as has been pointed out by Pfeffer (28). 
Further, the processes of nuclear and cell-division are 
independent of each other as is most clearly shown in Clado- 
phora , for the lower plants, and in certain types of endosperm- 
formation in the Phanerogams. From this standpoint we can 
still further sharpen our distinction between cells and tissues 
